[SPARK-3555] Fix UISuite race condition

The test "jetty selects different port under contention" is flaky.

If another process binds to 4040 before the test starts, then the first server we start there will fail, and the subsequent servers we start thereafter may successfully bind to 4040 if it was released between the servers starting. Instead, we should just let Java find a random free port for us and hold onto it for the duration of the test.

Author: Andrew Or <andrewor14@gmail.com>

Closes #2418 from andrewor14/fix-port-contention and squashes the following commits:

0cd4974 [Andrew Or] Stop them servers
a7071fe [Andrew Or] Pick random port instead of 4040
[Minor]ignore all config files in conf

Some config files in ```conf``` should ignore, such as
        conf/fairscheduler.xml
        conf/hive-log4j.properties
        conf/metrics.properties
...
So ignore all ```sh```/```properties```/```conf```/```xml``` files

Author: wangfei <wangfei1@huawei.com>

Closes #2395 from scwf/patch-2 and squashes the following commits:

3dc53f2 [wangfei] duplicate ```conf/*.conf```
3c2986f [wangfei] ignore all config files
[Docs] Correct spark.files.fetchTimeout default value

change the value of spark.files.fetchTimeout

Author: viper-kun <xukun.xu@huawei.com>

Closes #2406 from viper-kun/master and squashes the following commits:

ecb0d46 [viper-kun] [Docs] Correct spark.files.fetchTimeout default value
7cf4c7a [viper-kun] Update configuration.md
SPARK-3177 (on Master Branch)

The JIRA and PR was original created for branch-1.1, and move to master branch now.
Chester

The Issue is due to that yarn-alpha and yarn have different APIs for certain class fields. In this particular case,  the ClientBase using reflection to to address this issue, and we need to different way to test the ClientBase's method.  Original ClientBaseSuite using getFieldValue() method to do this. But it doesn't work for yarn-alpha as the API returns an array of String instead of just String (which is the case for Yarn-stable API).

 To fix the test, I add a new method

  def getFieldValue2[A: ClassTag, A1: ClassTag, B](clazz: Class[_], field: String,
                                                      defaults: => B)
                              (mapTo:  A => B)(mapTo1: A1 => B) : B =
    Try(clazz.getField(field)).map(_.get(null)).map {
      case v: A => mapTo(v)
      case v1: A1 => mapTo1(v1)
      case _ => defaults
    }.toOption.getOrElse(defaults)

to handle the cases where the field type can be either type A or A1. In this new method the type A or A1 is pattern matched and corresponding mapTo function (mapTo or mapTo1) is used.

Author: chesterxgchen <chester@alpinenow.com>

Closes #2204 from chesterxgchen/SPARK-3177-master and squashes the following commits:

e72a6ea [chesterxgchen]  The Issue is due to that yarn-alpha and yarn have different APIs for certain class fields. In this particular case,  the ClientBase using reflection to to address this issue, and we need to different way to test the ClientBase's method.  Original ClientBaseSuite using getFieldValue() method to do this. But it doesn't work for yarn-alpha as the API returns an array of String instead of just String (which is the case for Yarn-stable API).
[Docs] minor grammar fix

Author: Nicholas Chammas <nicholas.chammas@gmail.com>

Closes #2430 from nchammas/patch-2 and squashes the following commits:

d476bfb [Nicholas Chammas] [Docs] minor grammar fix
[SQL][DOCS] Improve table caching section

Author: Michael Armbrust <michael@databricks.com>

Closes #2434 from marmbrus/patch-1 and squashes the following commits:

67215be [Michael Armbrust] [SQL][DOCS] Improve table caching section
[SPARK-1455] [SPARK-3534] [Build] When possible, run SQL tests only.

If the only files changed are related to SQL, then only run the SQL tests.

This patch includes some cosmetic/maintainability refactoring. I would be more than happy to undo some of these changes if they are inappropriate.

We can accept this patch mostly as-is and address the immediate need documented in [SPARK-3534](https://issues.apache.org/jira/browse/SPARK-3534), or we can keep it open until a satisfactory solution along the lines [discussed here](https://issues.apache.org/jira/browse/SPARK-1455?focusedCommentId=14136424&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14136424) is reached.

Note: I had to hack this patch up to test it locally, so what I'm submitting here and what I tested are technically different.

Author: Nicholas Chammas <nicholas.chammas@gmail.com>

Closes #2420 from nchammas/selective-testing and squashes the following commits:

db3fa2d [Nicholas Chammas] diff against master!
f9e23f6 [Nicholas Chammas] when possible, run SQL tests only